The area of a sheet of length $10.2 \,cm$ and width $6.8 \,cm$ expressed up to the proper number of significant figures is ......... $cm^2$.

Assertion $(A)$: The number $0.00764$ has three significant figures.
Reason $(R)$: If the number is less than $1$,the zeros on the right of the decimal point but to the left of the first non-zero digit are not significant.

Three measurements are made as $18.425 \, cm$,$7.21 \, cm$,and $5.0 \, cm$. The addition should be written as ........ $cm$.

The addition of three masses $1.6 \,g$,$7.32 \,g$,and $4.238 \,g$,expressed to the proper number of decimal places,is ....... $g$.

What is a significant number? What is a significant digit?

Keeping the significant figures in view, the sum of the physical quantities $52.01 \ m$, $153.2 \ m$, and $0.123 \ m$ is: (in $m$)